1989 Jaguar XJ6 Vanden Plas

I have a 1989 Jaguar XJ6 Vanden Plas 4 door sedan. 150,000 miles and a V6 engine. A light comes up and tells me "low brake pressure". I added fluid, but it still sayes that and there is no leaks or anything. Also, the car starts moving to the side a little when im accelerating like it needs alignment or something and I hear an exhaust sound whenever I let go of the gas. Please let me whats up.